diff --git a/zconf.h b/zconf.h
index 97b3a70..76aba96 100644
--- a/zconf.h
+++ b/zconf.h
@@ -439,7 +439,7 @@ typedef uLong FAR uLongf;
  * both "#undef _LARGEFILE64_SOURCE" and "#define _LARGEFILE64_SOURCE 0" as
  * equivalently requesting no 64-bit operations
  */
-#if defined(LARGEFILE64_SOURCE) && -_LARGEFILE64_SOURCE - -1 == 1
+#if defined(_LARGEFILE64_SOURCE) && -_LARGEFILE64_SOURCE - -1 == 1
 #  undef _LARGEFILE64_SOURCE
 #endif
 
@@ -447,7 +447,7 @@ typedef uLong FAR uLongf;
 #  define Z_HAVE_UNISTD_H
 #endif
 #ifndef Z_SOLO
-#  if defined(Z_HAVE_UNISTD_H) || defined(LARGEFILE64_SOURCE)
+#  if defined(Z_HAVE_UNISTD_H) || defined(_LARGEFILE64_SOURCE)
 #    include <unistd.h>         /* for SEEK_*, off_t, and _LFS64_LARGEFILE */
 #    ifdef VMS
 #      include <unixio.h>       /* for off_t */
diff --git a/zconf.h.cmakein b/zconf.h.cmakein
index 3c44906..8f1956c 100644
--- a/zconf.h.cmakein
+++ b/zconf.h.cmakein
@@ -441,7 +441,7 @@ typedef uLong FAR uLongf;
  * both "#undef _LARGEFILE64_SOURCE" and "#define _LARGEFILE64_SOURCE 0" as
  * equivalently requesting no 64-bit operations
  */
-#if defined(LARGEFILE64_SOURCE) && -_LARGEFILE64_SOURCE - -1 == 1
+#if defined(_LARGEFILE64_SOURCE) && -_LARGEFILE64_SOURCE - -1 == 1
 #  undef _LARGEFILE64_SOURCE
 #endif
 
@@ -449,7 +449,7 @@ typedef uLong FAR uLongf;
 #  define Z_HAVE_UNISTD_H
 #endif
 #ifndef Z_SOLO
-#  if defined(Z_HAVE_UNISTD_H) || defined(LARGEFILE64_SOURCE)
+#  if defined(Z_HAVE_UNISTD_H) || defined(_LARGEFILE64_SOURCE)
 #    include <unistd.h>         /* for SEEK_*, off_t, and _LFS64_LARGEFILE */
 #    ifdef VMS
 #      include <unixio.h>       /* for off_t */
diff --git a/zconf.h.in b/zconf.h.in
index 97b3a70..76aba96 100644
--- a/zconf.h.in
+++ b/zconf.h.in
@@ -439,7 +439,7 @@ typedef uLong FAR uLongf;
  * both "#undef _LARGEFILE64_SOURCE" and "#define _LARGEFILE64_SOURCE 0" as
  * equivalently requesting no 64-bit operations
  */
-#if defined(LARGEFILE64_SOURCE) && -_LARGEFILE64_SOURCE - -1 == 1
+#if defined(_LARGEFILE64_SOURCE) && -_LARGEFILE64_SOURCE - -1 == 1
 #  undef _LARGEFILE64_SOURCE
 #endif
 
@@ -447,7 +447,7 @@ typedef uLong FAR uLongf;
 #  define Z_HAVE_UNISTD_H
 #endif
 #ifndef Z_SOLO
-#  if defined(Z_HAVE_UNISTD_H) || defined(LARGEFILE64_SOURCE)
+#  if defined(Z_HAVE_UNISTD_H) || defined(_LARGEFILE64_SOURCE)
 #    include <unistd.h>         /* for SEEK_*, off_t, and _LFS64_LARGEFILE */
 #    ifdef VMS
 #      include <unixio.h>       /* for off_t */